The United States Patent Office issued a patent To Google this week that enables their self driving cars to automatically detect police vehicles based on the pattern of flashing lights on the police cars when they are running with lights and siren.
Once a police vehicle is detected, the self-driving car maneuvers itself to yield to the police vehicle; for example, by pulling over to a side of a road.
The system can also be used to detect other types of emergency vehicles such as ambulances based on ambulance light patterns.